PECAM1 and acute kidney injury: These investigations provided evidence of an extremely rare contribution of iEPCs to direct endothelial replacement, and the marked expression of the mature endothelial cell marker CD31 in all recruited iEPCs was noted; therefore, we measured circulating angiogenesis-related proteins to determine whether paracrine mechanisms underlie systemic-iEPC-therapy-induced maintenance of microvasculature in AKI kidneys.